Field of the Invention
The present disclosure relates to an image formation apparatus and particularly to a structure of a fixation apparatus included in the image formation apparatus.
Description of the Related Art
An image formation apparatus of an electrophotography type has widely been used. The image formation apparatus of the electrophotography type performs as printing steps, the steps of transferring a toner image in accordance with an input image to paper and fixing the transferred toner image onto paper. The toner image is fixed by a fixation apparatus mounted on the image formation apparatus.
Some fixation apparatuses include two belts without end (hereinafter also referred to as an “endless belt”). Hereinafter, one of the two endless belts is also referred to as a first endless belt and the other is also referred to as a second endless belt. A pressurization member is provided inside the first endless belt. The pressurization member is fixed inside the first endless belt, and the first endless belt and the second endless belt are brought in contact with each other by pressurizing the first endless belt toward the second endless belt.
In the step of fixing a toner image, the fixation apparatus rotates at least one of the first endless belt and the second endless belt while the belts are heated, and pressurizes and heats paper which passes between the first endless belt and the second endless belt. The toner image on paper is thus fixed onto the paper. Since the endless belt is in a form of a belt, an area of a portion of contact between the first endless belt and the second endless belt (hereinafter also referred to as a “nip portion”) increases and heat is efficiently transferred to paper at the nip portion. Power consumption is thus suppressed.
In connection with a fixation apparatus including an endless belt, Japanese Laid-Open Patent Publication No. 2014-197076 discloses a fixing device “with a simple structure that prevents a failure of sheet conveyance at the sheet entry position.” Japanese Laid-Open Patent Publication No. 2010-217457 discloses a fixing device “which solves problems of misalignment of an image and displacement of a belt to the left or right due to a difference in peripheral speed.”
The fixing device disclosed in Japanese Laid-Open Patent Publication No. 2014-197076 includes a pressure belt and a fusing belt as endless belts. A drive roller for rotationally driving the pressure belt is provided inside the pressure belt. As the drive roller rotationally drives the pressure belt, driving force is transmitted to the fusing belt in contact with the pressure belt. Since the fusing belt is not in direct contact with the drive roller, a difference in driving force is caused between the fusing belt and the pressure belt. Consequently, a difference in peripheral speed is caused between the fusing belt and the pressure belt, which leads to image misalignment or paper slippage.
The fixing device disclosed in Japanese Laid-Open Patent Publication No. 2010-217457 includes a first belt and a second belt as endless belts. A recess portion and a projection portion are provided along a direction of rotation at opposing ends of the first belt and the second belt, the recess portion and the projection portion being constructed to fit into each other during rotation. The fixing device thus suppresses a difference in peripheral speed between the first belt and the second belt. In order to realize this, however, projections and recesses should be provided at the opposing ends of the first belt and the second belt, and cost for manufacturing the fixing device increases. Since stress is concentrated to the projection and recess portions, durability is low.
Therefore, a fixation apparatus capable of suppressing a difference in peripheral speed between at least two endless belts with a construction more simplified than in a conventional example is desired.